Manufacture of leather sheets containing normally tacky impregnating agents



United States atent MANUFACTURE OF LEATHER SHEETS CONTAIN- IfiNIIORMALLY TACKY IMPREGNATING Lucius H. Wilson, Riverside, Conn., assignor to American cg'la lnamid Company, New York, N. Y., a corporation me No Drawing. v Application October 28, 1952, Serial No. 317,358

6 Claims. (Cl. 92-21) This application is a continuation-in-part of my copending application Serial No. 287,801, filed May 14, 19

The present invention relates to the manufacture of leather sheets from leather fibers. More specifically, the present invention relates to the manufacture of strong, well-bonded leather sheets prepared from leather fibers by forming an aqueous suspension of leather fibers, adding to said suspension at dimethylolurea water-soluble polyfunctional nitrogen base resin in the hydrophilic stage as a colloidal cationic aqueous dispersion thereof, absorbing the resin on the fibers, and then adding an aqueous dispersion or emulsion of a normally tacky or sticky impregnating agent and depositing the impregnating agent on the fibers by the action of the adsorbed cationic resin. The present invention provides a method for forming impregnated leather sheets in this manner While avoiding formation of fibrous strings, balls or aggregates, hereinafter termed clots, during and after deposition of the impregnating agent, as described.

The coating or impregnating of leather fibers with organic hydrophobic impregnating agents has been performed in the past by preparing an aqueous stock or suspension of the fibers, adding to the stock an aqueous colloidal dispersion of a cationic melamine-aldehyde resin, and then adding the impregnating agent in the form of an aqueous emulsion or dispersion. The melamine-aldehyde resin is adsorbed by the fibers and causes a very uniform deposition of the particles of the impregnating agent directly on the fibers, while preserving the drainage qualities and the felting properties of the stock. By means of this process, it has been found feasible to produce leather sheets which contain large amounts of the impregnating agent. The sheets obtained are characterized by the uniformity of their content of impregnating agent, and in this process at most a negligible proportion of the impregnant is lost in the white water. Such a process is disclosed and claimed in U. S. Patent No. 2,601,671 of which I am coinventor.

The reason for the success of the above-described process in causing deposition of the impregnating agent while maintaining the freeness of the fibers has not been fully understood. It is believed, however, that the chief effect produced by the several steps involved are these. The cationic melamine-aldehyde resin, which is always added first, is very strongly positively charged and either reduces any negative charge on the fibers or converts the fibers to a more positively charged state. The dispersion of impregnating agent is defiocculated in the immediate presence of the more positively charged fibers, causing uniform and substantially complete deposition of the impregnating agent directly thereon. That other mechanisms exist, however, is demonstrated by the fact that excellent deposition of the'resin occurs in numerous instances when the emulsion or dispersion of the impregnating agent is added before more than a negligible amount of the cationic resin has been adsorbed by the fibers.

The melamine-aldehyde resins referred to, while yielding excellent results, have been found to possess a number of collateral disadvantages. The melamine component itself is costly and finds critical employment in the military economy. Moreover, the resin is not stable as prepared, but as a practical matter must be spray dried to a substantially anhydrous powder. Then, before the powder can be used, it must be dissolved in acid and the solution or suspension aged.

The resins disclosed in U. S. Patent No. 2,554,475 to T. J. Suen et al., are free from the foregoing disadvantages while possessing sufiicient cationic properites to render them useful as precipitants in the same manner as melamine-aldehyde resins. The resins described therein, hereinafter termed "dimethylolurea-nitrogen base resins or dimethylolurea-polyalkylenepolyamine resins are readily prepared by mixing formaldehyde, urea, and a polyfunctional organic nitrogen base, preferably a polyalkylenepolyarnine, and heating the mixture, first at an alkaline pH to form dimethylolurea and then at pH l-2 to cause the nitrogen base to combine. Formation of a cationic syrup is complete after 1-2 hours of heating at 7090 C. The syrup is stabilized merely 'by the addition of caustic, and it need not be spray-dried. To prepare the syrup for application to fibers it need be only diluted with water, and the resulting dispersion or solution need not be aged. Urea and formalin are noncritical materials, which are cheap and in abundant supply. The preferred nitrogen base is a polyalkylenepolyamine, and only a small amount is needed, typically 10% of the weight of the urea. Thus from the points of view of ease of preparation and cost of raw materials, the urea-formaldehyde-polyalkylenepolyarnine resins appeared to mark a significant step'forward in the art.

However, it has been found that when resins of this type are added to a stock of leather fibers, followed by addition of an emulsion or dispersion of a hydrophobic impregnating agent in the normally soft, tacky stage, the dispersion of fibers begins to clot before more than a small amount, for example, 10% based on the weight of the leather fibers, of the impregnating agent is added. Typically, this clotting begins by formation of the fibers into loose stringy bundles. Even these loose bundles are very difficult to felt and turn out a weak and stringy sheet. Upon addition of further amounts of the impregnating emulsion the bundles form into ropes which then clot together. When about 15% of impregnant has been added, based on the weight of leather fibers, the entire mass of fibers forms a ball which is almost puttylike in consistency.

Despite numerous attempts, it has not been found practical to defiocculate these clots so as to regenerate a useful stock of leather fibers which can be formed into a waterlaid sheet in a papermaking machine. Up to the present, once any noticeable clotting has taken place in the stock, it has been necessary to discard the stock completely.

The cause of this clotting appears to be due to two factors. The first is that dimethylolurea-polyfunctional nitrogen base resins of the type described possess a much weaker cationic charge than the melamine-aldehyde resins previously used. As a result, the treated fibers less strongly repel each other, and after addition of the impregnant, tend to arrange themselves in parallelism. The second is the adhesiveness developed by the fibers after they have been coated by the normally tacky impregnating agent. Being only weakly mutually repellent, the impregnated fibers readily cohere.

The emulsions or dispersions of impregnating agents which so far have caused the most severe clotting to leather stocks are natural rubber latex, and synthetic rubher latices, and emulsions of acrylate esters polymerized to the soft tacky stage. Chief among the synthetic latices are the emulsions formed by copolymerizing butadiene and styrene, styrene and ethyl acrylate, butadiene and acrylonitrile, vinyl acetate and ethyl acrylate, and acrylic acid esters and isobutylene. These represent the principal commercially important synthetic rubbers and include the rubbers known as GRS, Buna-N, Buna-S, Hycar, GR-N, and Ameripol. In general, interpolymers whichcontain more than 50% butadiene or ethyl acrylate are sufficiently tacky to cause clotting, while of course the homopo'lymers themselves are particularly effective in this regard.

As a rule, the emulsions or latices which are most frequently responsible for the formation of clots are those which, when dried on a glass plate at room temperature, yield films which are tacky to the touch. However, clotting frequently takes place with emulsions which contain a somewhat less tacky impregnating agent. For example, clotting has been observed even during the application of emulsions formed from impregnating agents which are sufficiently tacky that films thereof, while only slightly tacky to the touch, mutually cohere when lightly pressed together. These include impregnants which are only sufliciently tacky to cause blocking, i. e., the undesirable sticking together of paper impregnated thereof.

The discovery has now been made that emulsions of normally tacky impregnating agents can be deposited on leather fibers following the application of a dimethylolurea-polyfunctional nitrogen base resin without causing the fibers to clot by first stabilizing the emulsion with a small amount of a non-ionic dispersing agent. The amount of non-ionic agent necessary for stabilization varies between about 1% and of the weight of impregnant in the emulsion, a larger amount within the range usually being required when the stock contains impurities and when a large amount of colloidal cationic resin is 'added.

When less than 1% is added, clotting may be expected, particularly when large proportions of impregnant are applied. At the other extreme, no added benefit results when more than 10% of non-ionic agent is added.

It has been further found that slightly better results are often obtained when an anionic dispersing agent is added as stabilizer along with the non-ionic dispersing agent, the anionic agent maintaining the fibers in a more open state during drainage and yielding a sheet in which the fibers are more uniformly dispersed. The amount of anionic dispersing agent so added should not be more than the weight of the non-ionic dispersing agent, and does not replace any part thereof. When more than this proportion of anionic agent .is added, it becomes increasingly difficult to effect complete precipitation of the impregnating agent on the fibers. Best results are obtained in terms of clarity of the white water, speed of drainage, and uniformity of fiber pattern of the product, by the use of a mixture of non-ionic and anionic agents, wherein the weight of the anionic agent is between about 25% and 100% of the weight of the non-ionic agent and when the weight of the non-ionic agent is between 1% and 10% of the weight of the leather fibers.

It is important that the stabilizing surface-active agent or agents be added directly to the emulsion, as adding the dispersing agents to the stock of leather fibers will not produce the desired results. V

The effect of the stabilizing agent or mixture of agents on the emulsion and on the mechanism whereby the emulsified impregnating agent is deposited on the fibers, and the reason why clots do not form in the process of the present invention are not understood and the invention should not be limited by any particular theory.

In the process of the present invention, deposition of the impregnating agent is rapid and usually complete, particularly in the case of natural rubber latex. Incomplete precipitation, when it occurs, is considered associated with the presence of excessive amounts of anionic surfaceactive agent in the latex, and it is a feature of the present invention that the effect of this excess agent may be offset Wholly or in substantially part by incorporating a small amount of papermakers alum in the emulsion after addition of the surface active agents. Only a few percent of alum, based on the weight of the impregnant, is needed and 5% of alum on this basis is the most that has ever been found necessary.

The leather fibers with which the above impregnating agents are incorporated may be obtained from any suitable source, and include leather tanned by any suitable procedure. Vegetable tanned leather, chrome tanned leather, alum tanned leather, as well as leather prepared by aldehyde tannages, aromatic sulfonic acid tannages, iron tannages and the like may be used either singly or in admixture.

More in detail, the process in its preferred embodiment is performed as follows. First a stock of leather fibers is formed at any ordinary consistency, for example, 0.5% to 5% or more. The fibers used ordinarily will be mechanically disintegrated leather scrap, but any thoroughly defibered leather may be used. To this is added a predetermined amount of a cellulose substantive, cationic, hydrophilic resin of the type described, at least suificient to cause deposition of the impregnating agent from the subsequently-added emulsion. The pH of the stock during addition of the resin should be below 7, but since the isoelectric point of leather is about 4.2, the pH most advantageously will be distinctly acid. The addition of more resin than is sufiicient to satisfy the adsorptive capacity of the leather should be avoided, as such amounts remain in the aqueous phase of the stock and disadvantageously deflocculate the emulsion before it has contacted the fibers. At least about 5% of resin based on the weight of impregnant should be added, and it is almost never necessary to add more than 15% to secure complete deposition. Generally, 10% of resin based on the weight of impregnating agent in the emulsion to be added causes very satisfactory precipitation while avoiding the danger of adding too little.

Absorption of the cationic resin by the fibers is rapid, but is is advantageous to allow the stock to age about 10 minutes or until the last traces of the resin have been adsorbed from the aqueous phase.

Upon completion of the deposition or flocculation of the emulsified impregnating agent, the stock of leather fibers is substantially unaltered in texture and color and consists of unaggregated leather fibers in a state of free and substantially complete dispersion.

The stock is then sheeted and dried by any ordinary means. Preferably the stock will be diluted with water to a consistency of about 0.5 and then sheeted to a felted product on a wire. Drainage of water is very rapid.

Thereafter, the sheets are dried, but because of the sensitivity of leather to heat and rapid drying, temperatures sufficiently high to cure or vulcanize the impregnant are generally disadvantageous and temperatures below 150 F. are preferred. Even when the sheets are dried at room temperature, that is, at about 25 C., a tough, well-bonded product is obtained. Such an air-dried sheet is extremely flexible and resilient, and has a distinctly springy feel.

The water-laid, drained sheets may be pressed between blotters through heavy calendering rolls to obtain a thick, heavy, extremely strong sheet of bonded fibers. Such a sheet, when similarly dried, displays excellent strength and wearing properties.

From the foregoing, it will be evident that the principal product of the present invention is a sheet of leather fibers containing between about 0.5% and 10% of their weight of a dimethylolurea-polyfunctional nitrogen base resin and from about 15% to of their weight of a hydrophilic, normally tacky impregnating agent.

The cationic resins employed are prepared by conmam densing a urea-formaldehyde reaction product under acid conditions, and preferably at pH values below 40-45, in the presence of a cationic nitrogen-containing organic compound which is capable of condensing therewith. The preferred cationic organic nitrogen compounds which are capable of condensing with dimethylolurea or other urea-formaldehyde reaction products are water-soluble polyfunctional organic nitrogen bases, i. e., compounds having the ability to copolymerize with dimethylolurea under acid conditions. Typical examples of such polyfunctional organic bases are the alkylene polyamines of the formula:

H2N(CnH2n.HN)xH in which x is one or more, such as ethylenediamine, 1,3- p roylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, the corresponding polyproylenepolyamines and polybutylenepolyamines, also guanidines, b'iguanides, condensation products of alkylenepolyamines (such as those above) with halohydrins such as alpha-dichlorhydrin, epichlorhydrin and the like, monoalkylolamines, dialkylolamines and the like, and the watersoluble condensation products thereof with aldehydes such as formaldehyde. By condensing these and similar polyfunctional cationic organic bases with dimethylolurea and similar primary or substantially monomeric urea-formaldehyde condensation products, obtained under slightly alkaline conditions by condensing urea or thiourea with formaldehyde, in the presence of sufiicient acid to reduce the pH to values of about 1.0 to 4.0, and preferably to about 1.0 to 2.5, measured after the reaction has proceeded for some time, there are obtained cationic urea-formaldehyde resins which are substantive toward cellulosic materials and can be used in the process of my invention.

The relative proportions of polyalkylenepolyamine and primary urea-formaldehyde condensation product may be varied over a wide range. Thus a resin containing of a polyalkylenepolyamine based on the urea employed gives very good results. More may be used up to 100% or more of the weight of urea.

The polymerized resin syrup is preferably neutralized to a pH on the order of about 6-7 in order to obtain a product which is stable on storage. Resin syrups prepared by this method are both Water-soluble and water dilutable, and also can be evaporated to dryness and redissolved in water without substantial reduction in their water solubility.

Any non-ionic dispersing or emulsifying agent may be used in the present invention. Suitable agents of this class include the reaction products of fatty alcohols or fatty acids of 8-22 carbon atoms with 6 to 50 mols of ethylene or proylene oxide to yield compounds of the formula In addition, there may be employed condensates formed by reacting ethylene oxide or propylene oxide with a monoor polycarboxylic acid glycol or polyglycol esters. 'Ihus, mannitol or sorbitol may be mono-esterified with a fatty acid and the product reacted with 650 mols of ethylene oxide. Moreover, the condensation products of aryl, alkaryl, cycloaliphatic and arylcycloaliphatic alcohols and thioalcohols with 6-50 mols of ethylene oxide or propyene oxide to form dispersing agents may likewise be used. Such agents may have the formula In addition, the polyethylene glycol substituted maleic esters of the formula HO CHzO nCHZOCH COOR) CHZCOOR may be used.

The anionic dispersing agents employed may be any agent selected from the well-known group consisting of the alum-stable sulfonate and the alum-stable sulfate dispersing agents. Numerous members of this g'roupare well known in the detergent art and are characterized in that /2% aqueous solutions thereof do not precipitate or fiocculate at 20 C. in the presence of 500 p. p. m. of papermake-rs alum as aluminum sulfate tetradecyl hy= drate. Representative members of this group include the following:

Sodium alkylnaphthalene sulfonates condensed with form- I aldehyde Sodium isopropylnaphthalene sulfonate So'dium butylnaphthalene sulfonate Sodium tetrahydronaphthalene sulfonate Sodium monobutyl phenylphenol monosulfate Sodium alkylsulfobenzoate condensed with formaldehyde Purified sulfolignin Sodium alkyl phenylene sulfonate Sodium alkyl (ca. C11) sulfonate Sodium octyl sulfate Sodium aryl alkyl polyether sulfonate Sodium aryl alkyl ether sulfate Sodium alkylbenze-ne mono-sulfonates Sodium salt of N-oleyl-N-methyltaurine Sodium salt formaldehyde condensate of benzyl naphthalene sulfonic acid Sodium dodecyl phenyl poly (3) glycol ether sulfonate Sodium alkylanilinesulfonate Mixtures of the two or more nonionic dispersing agents and mixtures of two or more anionic dispersing agents of the above types may also be used.

The preparation of the emulsions or dispersions of tacky impregnating agents of the type described is very well known in the art. Briefly, they are made by forming an aqueous solution of an appropriate anionic surface active agent and a polymerization catalyst and stabilizer if desired, and then slowly pouring in the liquid monomer. The monomer simultaneously polymerizes and emulsifies in the water, which advantageously may have an elevated temperature. Ordinarily, suflicient monomer is added to form a dispersion having a solids content of about 40%60%. As dispersing agents, soaps are preferred because of their low cost and high effectiveness. Typical among these are sodium stearate, olea'te, palmitate and laurate; the sodium soaps of cocoanut fatty acids; sodium rosinate; the soaps of other rosin acids; and the sodium soap of disproportionated rosin.

The leather sheets of the present invention are suitable for use as materials for the manufacture of leather heels, leather soles, leather lining material, and sound absorbent leather flooring.

The invention has been completely disclosed above. The following specific examples represent prefenred embodiments of the invention and are not to be construed in limitation thereof. Parts are by weight unless otherwise stated.

Example 1 A solution of 678 g. of 37% formaldehyde and 200 g. of urea was adjusted to a pH of 8.3-8.8 with triethanolamine, and the mixture was thereafter heated at 70 C. for 30 minutes. 20 g. of tetraethylenep'entamine was then added to the mixture together with 47 g. of water, and after slight cooling, 55.7 g. of 18% hydrochloric acid, was then added to the mixture. The temperature of the mixture was brought to 70 C. and maintained at this point for 1 hour. The pH of the syrup was adjusted to 3.0 with aqueous NaOH and the temperature reduced to 55 C. The viscosity increased and the syrup was neutralized with 10% sodium hydroxide when its viscosity reached 200 cp. at 25 C. The syrup was then diluted to 10% solids with water.

A master batch of a stock of mechanically shredded vegetable tanned leather scrap was prepared by slurrying the fibers in water at about 4% consistency. The pH of the resulting stock was 3.5. The stock was divided into aliquots.

Test A.To one aliquot containing 50.0 g. of leather fibers was added 2.5 g. (solids basis) of the diluted resin and the mixture gently stirred and allowed to age for 10 minutes. To the suspension was added with gentle stirring natural rubber latex containing 25 g. of natural rubber to which had been added 0.6 g. of the non-ionic condensation product of tertiary octylphenol with 10 mo'ls of ethylene oxide. The rubber precipitated completely on the fibers, leaving a clear aqueous phase. After deposition was complete, the fibers appeared to be in their original state of freeness and no evidence of clotting was observed. The pH of the stock at this point was 6.0.

The fiber stock was placed in the deckle of a Nash hand-sheet machine, diluted to about 0.2% consistency with water and formed into a sheet by drainage. The sheet was pressed between blotters in a Noble-Wood press to a caliper of and air dried. A very tough, fiexible, resilient sheet closely resembling natural leather was obtained.

Test B.-The above procedure was repeated except that none of the octylphenol ethylene oxide condensation product was added to the latex. The latex was added in increments of about 2% of latex solids based on the dry weight of the fibers, and the condition of the stock was observed after each addition. When about 10% of latex rubber had been added, based on the weight of the fibers, deposition of the latex on the fibers became incomplete, the water becoming cloudy, and the fiber began to clot into long strings. When a total 15% latex rubber had been added, the fibers clotted to a dense putty-like ball, and the aqueous phase was opaque with latex.

Example 2 A stabilizing mixture of surface active agents was prepared by mixing 70 parts of the non-ionic agent formed by reacting tertiary octylphenol with 10 mols of ethylene oxide, with 30 parts of the anionic agent formed by condensing sodium alkylnaphthyl sulfonate with formaldehyde.

Test A.-The procedure of test'A of Example 1 was 7 repeated, except that 125 g. of the above-described mix- Example 3 To a Hycar OR-25 latex (formed by emulsion copolymerizing a mixture containing 75% of butadiene and 25% acrylonitrile by weight) was added 2.5 g. of the stabilizing mixture of Example 2, plus alum based on the weight of latex solids. The emulsion was stable.

The procedure of test A of Example 2 was repeated but substituting an equal amount (solids basis) of the Hycar latex for the rubber latex used.

Precipitation of the Hycar on the leather fibers was rapid and complete, leaving a clear aqueous phase. The fibers were well dispersed and drained freely when sheeted. The sheet obtained was substantially identical in all respects to the sheets obtained in Examples 1 and 2.

Example 4 Test A.- -A polyethyl acrylate emulsion was prepared by adding over 3 hours 35 parts of ethyl acrylate' to 60 parts of agitated water at about 82 C. The pH of the water was 8.5; it contained 5% of sodium olea'te'as the emulsifying agent and 0. 25% of ammonium persulfate as catalyst, based on the weight of the ethyl acrylate.

The emulsification was stopped 15 minutes after all the i ethyl a-crylate had been entered'and unreacted monomer was stripped ofi.

An aliquot of the leather stock of Example 1 containing 50 g. of leather fibers was treated with 5% of ureaform-aldehyde-tetraethylenepentamine resin according to Example 1. To this stock, after aging, was added a portion of the polyethyl acrylate emulsion containing 25 g. of ethyl acrylate equal to 50% of the weight of the leather fibers, and 1.8 g. of the stabilizing mixture of Example 2.

To the emulsion was then added 5% by weight of papermakers alum. When the emulsion was added to the resin treated leather fibers, deposition of the dispersed particles of polyethyl acrylate was rapid and complete, leaving a clear white water. The fibers were formed into a sheet in accordance with the method of Example 1 and 2, which was practically indistinguishable therefrom.

Example 5 The procedure of Example 4 was repeated, substituting, however, GRS-VI emulsion in place of polyethyl acrylate and reducing the amount of mixture of surface active agent to 5% of the solids content of the GRS-VI emulsion. The sheet obtained was substantially identical with the sheets of Examples l-4.

I claim:

1. In a method for making an impregnated leather sheet by the steps of preparing an aqueous stock of leather fibers, adding an aqueous colloidal dispersion of a normally tacky, water-insoluble hydrophobic organic impregnating agent containing a soap as principal dispersing agent therefor, depositing said impregnating agent on the fiberswhile in aqueous suspension, and forming the fibers into a sheet, the steps of first adding to the fiber suspension at pH between about 3 and 7 a colloidal cationic dimethylolurea water-soluble polyfunctional nitrogen base resin, then adding said aqueous dispersion of tacky impregnating agent containing, in addition, a non-ionic surface-active agent and an anionic surface-active agent selected from the group consisting of the alum-stable sulfonate and the alum-stable sulfate dispersing agents, and sheeting and drying the fibers; the weight of said impregnant being between about 15% and of the weight of the fibers; the weight of said cationic resin being'about 5% and 15% of the weight of said impregnant, the weight of non-ionic agent being between 1% and 10% of the weight of the fibers, and the weight of anionic surface-active agent being between 25% and 100% of the weight of non-ionic surfaceactive agent.

2. A process according to claim 1 wherein the resin is a dimethylolurea-polyalkylenepolyamine resin.

3. A process according to claim 1 wherein the impregnating dispersion is a butadiene-acrylonitrile copoly mer latex.

4. A process according to claim 1 wherein the impregnating dispersion is a butadiene-styrene co-polymer latex.

5. A process according to claim 1 wherein the impregnating dispersion is an ethyl acrylate polymer latex.

6. In a method of making an'impregnated leather sheet by the steps of preparing an aqueous stock of leather fibers, adding an aqueous colloidal dispersion of a normally tacky water-insoluble hydrophobic organic impregnating agent containing a soap as principal dispersing agent therefor, depositing said impregnating agent on the fibers while in aqueous suspension, and forming the fibers into a sheet, the steps of first adding to the fiber suspension at pH between about 3 and 7 a colloidal cationic dimethylolurea water-soluble polyfunctional organic nitrogen base resin, then adding said aqueous dispersion of tacky impregnating agent containing, in addition, alum, a non-ionic surface-active agent and an ani- Onic surface-active agent selected from the group con- 2,471,945 Figdor May 31, 1949 sisting of the alum-stable sulfonate and the alum-stable 2,516,284 Winheim et a1. July 25, 1950 sulfate dispersing agents, and sheeting and drying the 2,554,475 Suen et al. May 22, 1951 fibers; the weight of said impregnant being between about 2,601,598 Daniel et a1. June 24, 1952 15% and 100% of the weight of the fibers; the weight 5 2,601,671 Wilson et al. June 24, 1952 of anionic surface-active agent being between 25% and 100% of the weight of non-ionic surface active agent, FOREIGN PATENTS and the Weight of non-ionic agent being between 1% and 975,701 France O 17 1950 10% 0f the weight of the fibers, the weight of said alum being less than 5% of the weight of the impregnating 10 OTHER REFERENCES agent Miskel: Paper Trade 1., June 29, 1944, page 32.

References Cited in the file of this patent Losee: Canadian Chem. and Process Ind., September UNITED STATES PATENTS 1946 page 2,334,545 DAlelio Nov. 16, 1943 15 

1. IN A METHOD FOR MAKING AN IMPREGNATED LEATHER SHEET BY THE STEPS OF PREPARING AN AQUEOUS STOCK OF LEATHER FIBERS, ADDING AN AQUEOUS COLLOIDAL DISPERSION OF A NORMALLY TACKY, WATER-INSOLUBLE HYDROPHOBIC ORGANIC IMPREGNATING AGENT CONTAINING A SOAP AS PRINCIPAL DISPERSING AGENT THEREFOR, DEPOSITING SAID IMPREGNATING AGENT ON THE FIBERS WHILE IN AQUEOUS SUSPENSION, AND FORMING THE FIBERS INTO A SHEET, THE STEPS OF FIRST ADDING TO THE FIBER SUSPENSION AT PH BETWEEN ABOUT 3 AND 7 A COLLOIDAL CATIONIC DIMETHYLOLUREA WATER-SOLUBLE POLYFUNCTIONAL NITROGEN BASE RESIN, THEN ADDING SAID AQUEOUS DISPERSION OF TACKY IMPREGNATING AGENT CONTAINING, IN ADDITION, A NON-IONIC SURFACE-ACTIVE AGENT AND AN ANIONIC SURFACE-ACTIVE AGENT SELECTED FROM THE GROUP CONSISTING OF THE ALUM-STABLE SULFONATE AND THE ALUM-STABLE SULFATE DISPERSING AGENTS, AND SHEETING AND DRYING THE FIBERS; THE WEIGHT OF SAID IMPREGNANT BEING BETWEEN ABOUT 15% AND 100% OF THE WEIGHT OF THE FIBERS; THE WEIGHT OF SAID CATIONIC RESIN BEING ABOUT 5% AND 15% OF THE WEIGHT OF SAID IMPREGNANT, THE WEIGHT OF NON-IONIC AGENT BEING BETWEEN 1% AND 10% OF THE WEIGHT OF THE FIBERS, AND THE WEIGHT OF ANIONIC SURFACE-ACTIVE AGENT BEING BETWEEN 25% AND 100% OF THE WEIGHT OF NON-IONIC SURFACEACTIVE AGENT. 